It is known that spacer material such as alumina powder is dispersed in a liquid crystal display which consists essentially of two sheets made of plastic film to keep the space between the sheets constant. According to this prior art method, the liquid crystal display is fabricated by injecting liquid crystal material into the space between the sheets in a vaccuum while holding the spacer material between the sheets and then sealing the assembly.
Dispersion of spacer material in a liquid crystal cell is often used for liquid crystal displays whose two base sheets are made of glass. However, in case where this method is applied to a liquid crystal display whose two base sheets are made of film, when a load test is made for a long time, spacer material tends to collect around the electrodes. Accordingly, if a twisted nematic liquid crystal is viewed through a polarizing plate, one will note that the portion where the spacer is collected together is darker. When the amount of the dispersed spacer is large, namely 20 to 30 or more particles/mm.sup.2, this phenomenon becomes conspicuous. When liquid crystal material is injected, the device is sealed in such a condition that the liquid crystal layer is at a pressure slightly lower than the atmospheric pressure and hence the spacer is pressed between the sheets. When the quantity of the spacer is small, most of the particles cannot move because they are pressed between the sheets. When the quantity is large, however, particles of smaller diameters can easily move about among particles of larger diameters, and therefore they move around inside the liquid crystal layer, thereby causing local collection of spacer material.
THe aforementioned phenomenon is now discussed in somewhat more detail. When spacer alone is dispersed in large quantities and the device is put to a load test, the spacer tends to collect along a specific direction near the electrodes. In case where an upper sheet 1 was rubbed upwardly to the right at an angle of 45.degree. and a lower sheet was rubbed downwardly to the right at an angle of 45.degree., as shown in FIG. 1, the spacer collects in the hatched portion 3 as shown in FIG. 2 for the following cause. If many spacer particles exist in a liquid crystal display, when the device is energized, a number of disclinations are produced in a manner similar to cases where impurity atoms in a metal line up along crystalline grain boundaries, and the spacer collects on the disclinations. If the dislinations are formed like a ring, the spacer also collects in the form of a ring. The ring of the disclinations becomes smaller so that it may become stabler in terms of energy. The particles of spacer accordingly collect together. Also, when either sheet of film is physically moved for one cause or another, a number of disclinations are generated around the particles of spacer which act as nuclii, and as the disclinations disappear, the spacer collects. The boundary of the display portion of a liquid crystal display is a boundary of liquid crystal domains and is a kind of disclination. The disclinations which were created around the spacer particles are absorbed into this stable disclination at the boundary and so the particles collect on the boundary of the display portion. The direction of movement of the disclinations is understood as described below.
The disclinations in a liquid crystal layer are in contact with the upper and lower sheets of film. Taking into account the gravity, it is assumed that movement at the upper junctions is made with easier than movement at the lower junctions. During a load test, application of an alternating electric field wobbles the liquid crystal, moving the disclinations in the direction in which the upper sheet was rubbed. As a result, the particles of spacer are moved to the right at an angle of 45.degree. to the electrode in the display portion until they reach the boundary, whence they are discharged from the display portion one after another. Thus, the spacer is stored outside the liquid crystal cell. Outside the display pattern, the spacer gathers around the near boundary of the display portion as indicated by the hatched portion in FIG. 2. When spacer is not dispersed uniformly in the liquid crystal cell, even if the quantity of the spacer is less than 10 particles/mm.sup.2, some locations may become conspicuous somewhat.